1. Field of the Invention
The present invention relates to a zoom lens system, an interchangeable lens apparatus, and a camera system. In particular, the present invention relates to: a zoom lens system which is suitable as an imaging lens system in, so-called, an interchangeable-lens type digital camera system; and an interchangeable lens apparatus and a camera system each employing this zoom lens system.
2. Description of the Background Art
In recent years, interchangeable-lens type digital camera systems have been spreading rapidly. Such interchangeable-lens type digital camera systems (also referred to simply as “camera systems”, hereinafter) include: a camera body having an image sensor such as a CCD (Charge Coupled Device), a CMOS (Complementary Metal-Oxide Semiconductor) or the like; and an interchangeable lens apparatus having an imaging lens system for forming an optical image on a light receiving surface of the image sensor.
Such interchangeable-lens type digital camera systems are able to take a high-sensitive and high-quality image because an image sensor used in the interchangeable-lens type digital camera systems is larger than that equipped for a compact type digital camera. In addition, the interchangeable-lens type digital camera systems can realize: high-speed focusing and high-speed image processing after image taking; and easy replacement of an interchangeable lens apparatus in accordance with a desired scene. Furthermore, an interchangeable lens apparatus having a zoom lens system that forms an optical image with variable magnification is popular because it allows free change of focal length without the necessity of lens replacement. Accordingly, for some time, various kinds of zoom lens systems have been proposed, which can be utilized as an imaging lens system in the interchangeable-lens type digital camera systems, such as a zoom lens system disclosed in each of Japanese Laid-Open Patent Publications No. 2004-334185, No. 2001-117006, No. 2000-298236 and No. 2005-077917.
Although the interchangeable-lens type digital camera systems show the above-mentioned various kinds of merits, the size and the weight of such interchangeable-lens type digital camera systems are greater than those of a compact type digital camera. It is preferable that the size and the weight of the interchangeable-lens type digital camera systems are as small as possible for easy carrying around and handling. Accordingly, a most compact and lightweight possible zoom lens system with maintaining imaging performance is desired as a zoom lens system to be used in the interchangeable-lens type digital camera systems.